1. Field of the Invention
This invention is directed to a method and apparatus for testing, assisting, and teaching persons having poor central vision and central or paracentral scotomas to enable them to read words and see complex figures or images. More specifically, the invention is directed to a method and apparatus for initially testing individuals so as to determine and map various parameters associated with the central or paracentral visual field to determine the area or areas of the individual's visual field which can be best utilized, the functional visual fields, for specific tasks, such as for receiving visual data presented in the form of letters or words for reading. Thereafter, the individual is further tested so as to identify what effect contrast sensitivity has in the selected functional visual field and to further determine the effect that illumination and/or color may have with respect to perception within the functional field. Further tests are made to identify distortions of images in the functional visual field. The information is preferably obtained through an interactive system wherein the individual reacts to different images displayed on a monitor or screen or other image transmitting device.
Having tested and mapped an individual's functional visual fields and the effect various parameters have on the fields, visual images are modified with appropriate enhancements so as to individualize the images to be presented depending upon the mapped parameters. The optimized images are thereafter presented to the functional visual field of the individual in such a manner so as to maximize the individual's ability to improve reading speed and comprehension.
The present invention further enables an individual's mapped parameters to be used to simulate a modified image so that others having normal vision can perceive what a person with poor vision actually sees, thus enabling others to understand the limitations which the individual has in understanding visually presented information.
2. History of the Related Art
Persons with macular, central retinal, pathology have difficulty with their central vision due to absences, scotomas, or other distortions. Previously, optical and closed-circuit television devices that have been used to assist such persons to read or recognize faces or objects at a distance have relied primarily upon magnification to overcome the visual impairment and have done little or nothing to account for individual parameters which affect the ability to comprehend images such as distortions and alterations of contrast sensitivity within the visual field. Recent research indicates that a person's ability to read or to recognize faces depends not only on the detection of elements, such as letters or objects, but also the spatial integration of these elements. For example, for a person to recognize the face of a friend, such person must have intact a sufficiently large area of their visual field, retinal area, to be able to see most of the features of the face at one time. For a person to read, a certain field of view is required without defects in order to integrate individual letters into words in between eye movements from one group of letters or words to another. Even if central acuity is good, if there are multiple paracentral visual field defects such that fewer than four letters can be spanned in the field of view at one time, a person's reading is incumbered because they are unable to integrate sufficient letters to form words and are unable to know where to shift their view to a subsequent group of letters or words.
People with central scotomas and poor central vision who must successfully adapt with conventional vision aids are those who develop stable eccentric fixation. That is, they turn their eyes away from an object thereby displacing the central scotoma out of the way so the object can be imaged onto the area of the intact and functioning retina. However, stable eccentric fixation is infrequently adopted by people who lose their central vision, most often the elderly, and when spontaneously adopted, may be inappropriate for a particular task. For example, if a person develops an eccentric fixation position for reading which leaves the scotoma to the right of a point of fixation, reading languages in the western world remains severely incumbered as the ability to follow a series of letters to form a word which can be comprehended continues to be a difficult, if not impossible, task.
Previously, visual fields were mapped primarily by glaucoma specialists interested in abnormalities of the far peripheral field, peripheral to 60.degree., or by neurologists interested in gross defects of the optic neural tracts, a quarter or half of the entire visual field missing. These fields have been mapped utilizing only points of light of varying intensity and size that are moved to the visual field from nonseeing areas or projected in sequence unto a curved or flat screen in front of an individual while the individual's vision is concentrated or focused straight ahead. The individual signals the observation of briefly presented eccentric light sources by pressing an appropriate device such as an electronic button.
In the Humphrey Automated Visual Field, points of light are sequentially presented at previously defined intercepts over the visual field in a random fashion. Each point is retested with progressively increased intensity until a person signals that a light is perceived, or if the light has been previously received, by gradually decreasing the intensity of the light until it is no longer perceived. The individual's sight must be fixed straight ahead on a central target which is a difficult task for persons with poor central field vision. Therefore, in order to test such persons an examiner has the patient look straight ahead at a stationary large target and evaluates the ability of fixation by periodically testing a physiologic blind spot which is a 15.degree. eccentric scotoma in all persons. If a person responds to perception of light a significant number of times it is presented in the blind spot, there is an indication that fixation is unstable and that the field testing is unreliable. This is very common in individuals with central scotomas. However, by testing only points of light, the visual field is not evaluated for spacial integration or higher level processing that is required for visual tasks, such as character recognition in reading and facial recognition.
In another apparatus known as a scanning laser ophthalmoscope, a laser light is scanned rapidly over the retina in a raster pattern and is spatially attenuated in order to project, on the retina, spots or images of limited contrast and complexity. This instrument has been used in a limited manner to determine the ability of the retina to detect individual letters. The image is not stabilized on the retina; however, the examiner can view the retina simultaneously during the procedure so that a spot of light or image can be positioned in the retinal area of interest and any responses from the individual that occurred during unwanted eye movements, those away from a point of visual fixation, can be appropriately discarded. Unfortunately, this technique is laborious and has other severe restrictions.
The ability to perceive contrast centrally by an individual in relationship to spatial frequency has been previously tested by using letters of varying contrast or by using a sinusoidal gray scale grating projected on a monitor or screen or printed on a paper chart placed in front of the individual who looks directly at the letter or grating. The grating is usually presented at the central point of fixation in a circular area spanning 4.degree.-5.degree. of the central field. When letters are used, the contrast is varied up or down until the perception of each letter size is thresholded. If sinusoidal gratings are used, the contrast of light and dark bars against a background is varied until the individual signals that they are observed by indicating the orientation of the bars which are randomly presented at vertical, tilted left or right of vertical. The spacial distance or frequency is then changed by narrowing or widening the spacing between the bars, and the contrast is again varied until a threshold when the orientation of the grating is accurately perceived. The contrast sensitivity function for an individual is presented in a graph as a relationship between threshold contrast perceived at the center of fixation and the spacial frequency of the grating.
Conventionally, patients with retinal or optical nerve causes for reduced visual function frequently note that their vision is reduced under conditions of reduced illumination or that color affects their perception. Conventional testing for these parameters has been limited to measurements of central visual acuity at reduced light levels or with glare conditions or central fixation color matching or color image detection.
Heretofore, central visual field distortion has been subjectively evaluated by having a person visually fixate on the center of a grid of horizontal and vertical lines drawn on paper, known as an Amsler grid, as the person draws areas where there are distortion, such as waviness in lines. However, this technique is not quantitative and impossible to compare over time and does not lend itself to understanding an image in order to assist a patient with these encumbrances to comprehend information when presented.
In view of the foregoing, conventional methods of testing for poor central field vision have not taken into account the variety of secondary parameters which can affect an individual's limited vision within a functional field. Further, conventional methods of recreating and presenting information to individuals with poor central field vision have not recognized the need to modify images being presented so as to optimize the manner in which the images are received. Conventional methods have not incorporated contrast sensitivity, the effect illumination and/or color has on perception and the effect distortion has within a functional field of vision to modify image presentation and therefore have not been adequate to optimize the reception and comprehension of visual information.